Field of the Invention
The present invention relates to a method of dividing a wafer.
Description of the Related Art
Cutting apparatus for cutting a wafer with a cutting blade operate by holding the wafer adhered to an adhesive tape on the holding surface of a chuck table, thrusting the cutting blade which is rotating at a high speed to incise the wafer held on the chuck table, and cutting the wafer until the tip end of the cutting blade reaches the adhesive tape, thereby fully severing the wafer. The cutting apparatus are capable of fully severing the wafer because they recognize the vertical position of the holding surface of the chuck table holding the wafer and the vertical position of the tip end of the cutting blade (see, for example, Japanese Patent No. 4549654), calculate how deep the tip end of the cutting blade is to incise the adhesive tape from the reference position where the tip end of the cutting blade contacts the holding surface of the chuck table, depending on the thickness of the adhesive tape being used, lower the cutting blade until the tip end thereof reaches a position based on the calculated depth in an incising feed mode, and move (cutting feed mode) the cutting blade with respect to the wafer thereby to cut the wafer in a cutting feed mode.
The cutting blade that is used to cut the wafer has such a property that it is progressively worn as the cutting process continues. When the cutting blade has cut a certain amount of wafer in the cutting process, the actual depth by which the cutting blade has cut into the wafer is smaller than the calculated depth by which the cutting blade is to cut into the wafer. Therefore, when the cutting blade has cut a certain amount of wafer, the tip end of the cutting blade is detected again by position detecting means such as an optical sensor or the like, and the depth by which the cutting blade has incised the wafer is managed so that it will reach a depth required to fully sever the wafer (see, for example, Japanese Patent No. 5389604). Alternatively, when the cutting blade has cut a certain amount of wafer, the cutting blade is actuated in the incising feed mode, but not in the cutting feed mode, to incise a cut mark bearing workpiece to leave a cut mark thereon, then the diameter of the cutting blade is calculated from the length of the cut mark, and the depth by which the cutting blade has incised the wafer is managed so that it will reach a depth required to fully sever the wafer (see, for example, Japanese Patent Laid-Open No. 2013-27949).